Incorrect Projection

[sholloway]

Summary

The current projection pipeline is not correctly mapping to clip space on the Z-axis.

Desired Behavior

3D vertices need to go through a series of transformations.

1. Model Space to World Space
2. World Space to Camera Space
3. Camara Space to Clip Space
4. Clip Space to Window Space

The clip space is a 3D cube defined by it's three axes I, J, K where: Per: https://carmencincotti.com/2022-05-02/homogeneous-coordinates-clip-space-ndc/ Every vertex (x, y, z, w) has it's own clip space in which it exists. Where:

-w <= x <= w
-w <= y <= w
0 <=z <= w

Root Cause

• This is just a precision error or rounding error.
• The projection matrix is wrong.
• There may be an issue between right-hand vs left hand.

Possible Solutions

• Leverage a different projection matrix.
• Leverage the reverse-z projection matrix.
• Transition this to a compute shader after solving the math.

Resources

• Reverse Z (and why it's so awesome)
• WebGPU Reverse Z Example
• Nvidia: Depth Precision Visualized
• Reverse Z Cheatsheet